Combination tubular baffle with electroacoustic transducer



Dec. 21, 1965 F. MAssA 3,225,326

COMBINATION TUBULAR BAFFLE WITH ELECTROACOUSTIC TRANSDUCER Filed June 8, 1960 4 Sheets-Sheet 1 INVENTOR: F R A N K M A SSA ATT'Y Dec. 21, 1965 F. MASSA 3,225,326

COMBINATION TUBULAR BAFFLE WITH ELECTROACOUSTIC TRANSDUCER Filed June 8, 1960 4 Sheets-Sheet 2 FIG] FIG. 8 /-42 F|G.9 FIG. IO

' INVENTORI FRANK MASSA ATT'Y Dec. 21, 1965 F. MASSA 3,225,326

COMBINATION TUBULAR BAFFLE WITH ELECTROACOUSTIG TRANSDUCER Filed June 8, 1960 4 Sheets-Sheet 3 FIG. ll

FIG. I2

42 FIG. l4

INVENTOR: FRANK MASSA ATT'Y Dec. 21, 1965 F. MASSA COMBINATION TUBULAR BAFFLE WITH ELECTROACOUS'I'IC TRANSDUCER Filed June 8, 1960 FIG. I5

FIG. I?

FlG. l9

4 Sheets-Sheet 4 FIG. I6

INVENTOR: FRAN K M ASSA iii -w.

ATT'Y United States Patent 3,225,326 COMBINATION TUBULAR RAFFLE WITH ELECTROACOUSTIC TRANSDUCER Frank Massa, Cohasset, Mass., assiguor, by mesne assignments, to Dynamics Corporation of America, New York, N .Y., a corporation of New York Filed June 8, 1960, Ser. No. 34,731 21 Claims. (Cl. 340--8) This invention relates generally to electroacoustic transducers, and more particularly with new and improved sonar transducers for generating high power sound in deep water at frequencies in the lower or mid-audible range. Prior art sonar transducers which have been used for generating low frequency under water sound have been of relatively low efliciency and have been limited to use in shallow water.

One object of this invention is to provide an improved electroacoustic transducer capable of generating acoustic power levels of several hundred to several thousand watts and of operating at submerged depths of several hundred to several thousand feet of water.

Another object of this invention is to produce a very rugged structure capable of operating at large, low frequency amplitudes of vibration sufiicient to generate acoustic power densities of the order of approximately 10 watts per square inch of radiating surface.

A further object of this invention is to reduce the weight of the radiating portion of the vibrating system of a high power sonar transducer in order to increase the bandwidth of high efiiciency operation of the transducer.

A still further object of this invention is to provide for efficicnt coupling of the radiating surface of a transducer to the water at high hydrostatic pressure without the need of any pressure relief materials.

Another object of this invention is to produce an underwater transducer capable of efi'icient operation in the lower or mid-audio frequency range.

Still another object of this invention is the provision of a new and improved underwater transducer which is characterized by its extremely high uniformity and relatively low cost of production.

These and other objects of the invention are set forth with particularity in the appended claims. However, for a better understanding of the invention itself, together with further features and advanages thereof, reference is made to the accompanying description and drawings in which is shown several illustrative embodiments of the invention.

In the drawings:

FIGURE 1 is a vertical cross section of one illustrative embodiment of the new transducer construction;

FIGURE 2 is a view taken along the line 2-2 of FIG- URE 1;

FIGURE 3 is a vertical cross section of another illustrative embodiment of the invention;

FIGURE 4 is a view taken along line 44 of FIG- URE 3;

FIGURE 4A is a view taken along the line 4A4A of FIGURE 3;

FIGURE 5 shows a schematic assembly of the new transducer in a tubular baffle structure;

FIGURE 6 illustrates the directional radiation pattern of the transducer and bafiie arrangement of FIGURE 5;

FIGURE 7 shows a spaced axial array of two transducer assemblies constructed in accordance with FIG- URE 5;

FIGURE 8 illustrates the directional radiation pattern of the array of FIGURE 7;

FIGURE 9 shows the array of FIGURE 7 with the spacing between the elements reduced;

FIGURE 10 illustrates the directional radiation pattern of the array of FIGURE 9;

FIGURE 11 shows a closely spaced array of three transducer assemblies constructed in accordance with FIGURE 5;

FIGURE 12 illustrates the directional radiation pattern of the array of FIGURE 11;

FIGURES 13 and 14 are views of a bundle assembly of transducers constructed in accordance with FIG- URE 5;

FIGURES 15 and 16 are end and sectional side views, respectively, of another illustrative embodiment of baflle structure in combination with the new transducer;

FIGURES 17 and 18 are end and sectional side views, respectively, of still another illustrative embodiment of bafile and transducer assembly structure; and

FIGURES 19 and 20 are end and sectional side views, respectively, of still another illustrative embodiment of baflie and transducer assembly structure.

Referring now to the drawing and more particularly to FIGURES 1 and 2, the reference numeral 10 identifies a flat center plate having top and bottom surface which advantageously are ground to be parallel to each other. A stack 12 of bonded E-shaped laminations is attached by means of a high tensile strength cement, such as an epoxy type resin, to each fiat surface of center plate 10. A coil of wire 14 is placed into each E slot of the lamination stacks 12 and each coil of wire is solidly secured to its lamination stack 12 by means of an epoxy cast resin or other suitable means.

The coils of wire 14 are electrically connected to the sealed, insulated terminals 16 shown mounted through one end plate 18. A laminated magnetic armature assembly 20 is bonded. to the inner surface of each end plate 18, as illustrated, to establish a fixed air gap between each end of a stack 12 and its armature assembly 20. A housing structure 22, which in one preferred embodiment is cylindrical in shape, is bonded to the end plate 20 to complete the sealed outer housing assembly of the transducer 24.

A plurality of support springs 26 are dimensioned such that when the springs are secured to the parallel surfaces of plates 10 and 18 by means of epoxy cement or any other suitable means, equal air gaps result at each end of the magnet assembly between the parallel surfaces of magnetic armatures 12 and 20. The compliance of the springs 26 advantageously is such that its magnitude in combination with the mass of the transducer assembly will be at resonance at the desired frequency of operation of the transducer.

The actual method of assembling the transducer components may follow any suitable and convenient sequence. The figures of the drawing are only illustrative in nature and are intended to show the fundamental principles of the invention. For example, in the actual construction of one transducer embodiment in accordance with the invention, the springs 12 were secured to the surfaces of plates 10 and 18 by the use of bolts 30 in addition to epoxy cement, and the mating surfaces of the outer housing structure have been both dovetailed and dowelled to Patented Dec. 21, 1965 p increase the reliability of the transducer 24 when operating under high values of hydrostatic pressure. These and other mechanical details of construction have not been shown in the drawings to maintain the latter relatively simple for an easier understanding of the fundamental operating principles of the invention.

In the actual operation of the transducer 24 illustrated in FIGURE 1, a D.-C. polarizing current is sent through both coils 14 such that a flux density of approximately the same magnitude is established in each of the air gaps between the magnetic armatures I2 and 20. As a result of the unique magnetic circuit and spring mounting arrangement illustrated, the static magnetic forces of attraction are equal at both air gaps, and the inner magnetic structural assembly is in a balanced position of rest with respect to the outer housing structure of the transducer 24.

The coils 14 advantageously are connected such that when A.-C. current is superimposed on the D.-C. polarizing current and its polarity is positive, it adds to the D.-C. current in one coil and subtracts from the D.-C. current in the other coil. This causes the flux density to increase in one air gap and to decrease in the other, which, in turn, results in a relative displacement of the inner and outer magnetic structures in such a direction as to decrease the air gap where the flux density is in creased and to increase the opposite gap where the flux density is decreased. When the polarity of the A.-C. current through the coils 14 is reversed, the exitation of the air gaps is reversed so that the displacement of the transducer elements is reversed, thus completing the cycle.

The actual displacement of the outer portion of the transducer is determined by the relative values of the inner and outer masses of the transducer structure, which masses are separated by the support springs 26. In order to secure highest operating efficiency for the transducer 24, operating as an underwater sound source, it is desirable to hold the mass of the outer housing structure to a minimum value. At the same time, it is desirable to keep the mass of the inner portion of the transducer assembly as high as possible in order to minimize the relative displacement of the inner portion of the transducer with respect to the outer housing structure. The advantageous results of adjusting the relative masses of the two vibrating portions of the transducer 24, as indicated, include a higher efficiency of operation over a wider frequency band because of the reduced inertia of the lower outer mass in comparison with the radiation resistance of the water, which results in the lowering of the Q of the system. Another advantage that results from having a relatively light outer vibrating portion in comparison to the inner yibrating portion is that the amplitude of the springs will be kept at a minimum for a given fixed amplitude of vibration of the outer sound radiating portion of the transducer assembly. This means that higher acoustic power output can be achieved from the transducer for a given maximum spring deflection.

It will be obvious to those skilled in the art from the above description that the outer surface of the transducer 24 forms a pressure hull which will resist hydrostatic pressure during submergence of the transducer in deep water. The limit of operational depth is determined by the maximum permissible deflection of the end plates 18 or the buckling of the housing wall 22. For low frequency operation, in the region below a few kilocycles, and especially in the region below about one kilocycle, it is required that the area of the radiating face of the transducer becomes relatively large if efiicient acoustic coupling to the water is to be maintained. Whereas an underwater transducer may be satisfactorily provided for operation at frequency of a few kilocycles with an effective diameter of radiating surface of several inches, it becomes necessary that the diameter be in the region of a foot for frequencies of several hundred cycles, and even greater diameters for frequencies in the vicinity of one or two hundred cycles.

As the frequency region of operation for the transducer is lowered and the radiating area is increased, the deflection of an end plate 18 in FIGURE 1 increases very rapidly for a given hydrostatic pressure. It therefore is necessary to increase the thickness of the end plate 18 if the transducer is to operate satisfactorily in deep water. If the end plate thickness is increased to withstand higher pressures, the resultant added mass of the plate will deteriorate the performance of the transducer for the reasons previously mentioned. In order to solve this problem it is advantageous that the thick end plates be made to withstand the required static pressure and while at the same time greatly reducing the mass of the structure. In accordance with a feature of this invention, this desirable end is attained by the provision of a composite end plate structure as illustratively shown in FIGURES 3 and 4A of the drawings. Each thick end plate 18A comprises two mating bonded sections 34 and 36, each section being hollowed with a honeycomb grid structure as illustrated in FIGURE 4A. When the two sections 34 and 36 are bonded together with epoxy cement, or by any other suitable method, the composite structure will withstand high static pressures while keeping the mass at a minimum, thereby substantially improving the performance of the transducer.

The general details of the transducer assembly 24A shown in FIGURES 3 and 4 are somewhat similar to the basic transducer structure 24 described in FIGURE 1. The primary difference is that the transducer structure illustrated in FIGURE 3 shows a plurality of magnetic elements arranged for a larger transducer assembly. In FIGURES 3 and 4, several magnetic armature assemblies 12A are attached to the center plate 10A in a manner similar to the arrangement illustrated in FIGURE 1. The magnetic armatures 20A similarly are bonded to the flat surfaces of end plates 18A. Springs 26A are assembled and serve the same function described in FIGURE 1.

Although the illustrative transducer housing shown has been disclosed as cylindrical in shape, those skilled in the art will readily appreciate that transducer hon-sing structures may also be made with a rectangular shape. In the latter case, I have built up composite, hollowed side plates of a rectangular shape and have assembled a rectangular shaped center plate 10 within the rectangular housing structure 22. This arrangement results in a rectangular box-like transducer which can be closely packed for applications requiring very large underwater radiating surfaces. The cylindrical embodiment is preferable in some instances since it offers the light-est housing structure due to the high submerged strength of the thin cylindrical housing shell as compared to a fiat plate.

The operation of the transducer embodiment of FIG- URE 3 is substantially the same as the operation described in connection with the transducer embodiment of FIGURE 1. As alternating current is superimposed on the polarizing direct current through the coils 14A, oscillatory forces are generated similar to the forces generated in the structure of FIGURE 1 and the entire outer housing structure will oscillate as a unit at a frequency corresponding to the frequency of the alternating current. Those skilled in the art will appreciate that this oscillatory motion of the entire outer structure of the transducer can give rise to phase interference between the sound radiated from the opposite end face-s and unless steps are taken to prevent this interference the output of the transducer will be very low. One well known method for preventing such undesired underwater radiation from a vibrating surface is to cover the surface with a low acoustic impedance material such as cork or cell-tite foam rubber. The provision of this material serves to uncouple the surface from the relatively high acoustic impedance of the water and, as a result, the undesired radiation is prevented from taking lace.

Thus, if a sheet of low acoustic impedance material is placed over one of the end faces of the transducer embodiments of FIGURE 1 or FIGURE 3, for example, such destructive interference would be eliminated and only the sound from one end plate would be radiated. This well known method for shielding undesired radiation is not satisfactory in deep water where the hydrostatic pressure becomes great enough to collapse the air bubbles in the low acoustic impedance pressure release material and the shielding effects of material is destroyed.

In order to solve the problem of destructive interference from the opposite phase of vibration of both ends of the new transducer assemblies disclosed herein, a relatively simple tubular baflie structure advantageously is employed. As illustrated in FIGURE 5, the transducer 24 is mounted within a rigid tubular baffle 42 such that it will vibrate freely along the vertical axis of the tubular baffle when the transducer is supplied with electrical power. The tubular baflle 42 has a shoulder portion 44 at one end thereof against which the transducer is supported. Advantageously, a thin layer of compliant material 46, such as rubber, encloses and separates the tubular bafile 42 and the transducer 24 from physical solid contact with each other.

For optimum operation of this simple baffie structure, it has been found desirable to make the length of the tube such that the distance between the enclosed radiating face of the transducer 24 and the open end of the tubular bafile 42 is approximately one-half wavelength of the radiated sound at the fundamental frequency of operation. The effect of this baffle construction is to introduce a half wavelength delay in the pat-h through the tubular baffie which effectively causes the sound emanating from each end of the tubular baffle to be substantially in the same phase. The combination of transducer and baffie illustrated in FIGURE 5 provides a directional radiation pattern approximately as illustrated in FIGURE 6, said pattern being normal to the longitudinal axis of baffle 42 and transducer 24. As shown, the pattern is a surface of revolution about the vertical axis. The beam angle in the vertical plane is approximately 90 wide at the 6 db down points. In the horizontal plane the beam pattern is omnidirectional.

In accordance with a further feature of this invention, narrower beam angles may be obtained by mounting a plurality of transducer and baffie assemblies 42 in a spaced axially aligned array as illustrated in FIGURES 7, 9 and 11 of the drawing. The radiation pattern for each of these assemblies is illustrated in FIGURES 8, l0 and 12, respectively, the pattern being shown normal to the axis of the assemblies.

In FIGURE 7, two transducer and baffle assemblies 42 are shown in axial alignment and spaced one-half wavelength apart at the frequency of operation. This array is approximately equivalent to four point sources of equal intensity spaced along a line at one-half wavelength intervals. The directional characteristic for this array is approximately shown in FIGURE 8. The vertical angle at the 6 db down points is approximately 35. Secondary lobes of a magnitude approximately 11 db below the rnain lobe sensitivity also are introduced, as shown in FIGURE 8. t In order to reduce the magnitude of the secondary lobes, if this is desired, it is contemplated that the two spaced bathed transducer of FIGURE 7 may be brought closer together as indicated in FIGURE 9. This arrangement is equivalent to a shaded line array of three points spaced approximately one-half wavelength apart in which the intensity of the center element is twice the intensity of each end element. The effect of this shaded array is to substantially reduce the secondary lobes as illustrated in FIGURE 10. The vertical beam angle at the 6 db down points is approximately 65 for the arrangement of FIGURE 9.

Those skilled in the art will now appreciate that to obtain still narrower vertical beam angles and also shading for the reduction of the secondary lobe magnitudes, more assemblies 42 may be added to the vertical array. FIGURE 11 shows a closely spaced vertical line array of 3 transducer and tubular baffle assemblies 42 which results in the vertical directional pattern shown in FIG- URE 12. The vertical beam angle at the 6 db down points is 50 and the secondary lobes are approximately 23 db below the main beam intensity for the arrangement of FIGURE 11. It clearly is within the principles of the invention that the arrangement of FIGURE 7 or FIGURE 11 may be multiplied along the vertical axis to produce narrower beam angles if desired.

If the diameter of the radiating face of the transducer is very small compared to the wavelength of sound at the operating frequency, the efficiency of the single assembly 42 illustrated in FIGURE 5 will be low and the Q will be high because the radiation resistance due to the water load on the surface of the small area will be relatively small. Figures 13 and 14 of the drawing illustrate a mounting arrangement for increasing the radiation resistance on the surface of the transducer and for materially increasing its acoustic power output. Advantageously, a group of transducer and baffle assemblies 42, as illustrated in FIGURE 5, are bundled together as a group and are rigidly held by welding or any other suitable fastening technique. Metal straps 50 may be used as bands for holding the transducer assembly group together. By grouping the transducers and baffles, as illustrated in FIGURES l3 and 14, and driving the transducers from the same electrical power source the effect of the assembly group is for the radiating area to greatly increase. Accordingly, more acoustic power can now be radiated from each unit with lower amplitudes of vibration as compared to a single unit as illustrated in FIGURE 5.

The arrangement of FIGURES 13 and 14 proves very beneficial for high power underwater radiation of sound if the diameter of the individual transducer is made of the order of wavelength or less of the sound at the frequency of operation. Manifestly, the grouping illustrated in FIGURE 14 may be reduced or increased to accommodate any situation. The limit on the group should be such that the effective over-all diameter of the assembly should not exceed approximately to /3 wavelength of sound at the frequency of operation if the grouped transducer assemblies are to be used in line arrays to substitute for the single assemblies illustrated in FIGURES 7, 9 or 11. If the over-all assembled diameter of the transducer group, as illustrated in FIGURE 14, exceeds wavelength of sound at the operating frequency the total area can no longer be considered as a point in the line array and destructive intereference will become objectionable in the plane parallel to the radiating surfaces of the transducer group.

The baffle structure discussed inconnection with FIG- URE 5 comprises means for shifting the phase of the radiation from one face of the transducer such that two in-phase radiation surfaces were effectively established by virtue of the /2 wavelength delay introduced in the tubular baffie 42 is illustrated in FIGURE 5. It also was disclosed in connection with FIGURE 5 that the two inphase sources would be spaced approximately /2 wavelength apart in space and therefore would result in a toroidal directional pattern as illustrated in FIGURE 6.

For applications where it is desired that the radiation take place either omnidirectionally, as in a spherical source, or more or less unidirectionally along a particular axis of the structure it is a feature of this invention to utilize a variation of the tubular baffle embodiment illustrated in FIGURE 5 which may take the form shown in FIGURES l5 and 16. In this embodiment, the tubular member 52 is a U-shaped modification of the tubular baffie 42 illustrated in FIGURE 5. As a result of this U-shaped arrangement, the phase of the radiation from the innermost surface of the transducer is delayed by /2 wavelength in passing around the U-shaped passageway as illustrated by the arrow 66. Therefore, in-phase radiation is achieved from both faces of the tubular structure which lie substantially in the same plane. If the diameter of the transducer and baflie are made small compared to the wavelength, the radiation from the openings will be omnidirectional. If a group of the assemblies illustrated in FIGURE are formed into a composite multiple array with the openings of the various structures arranged substantially in one plane, the radiation from the large effective area will become directional and will form essentially a unidirectional beam whose sharpness is a function of the over-all diameter of the composite surface as compared to the wavelength of sound being radiated. If the composite diameter is large compared with the wavelength of sound, the beam will become relatively sharp, as is well known to those skilled in the art.

Another embodiment of the arrangement illustrated in FIGURE 16 is shown in FIGURES 17 and 18. In this case, a reverse bathe structure is achieved by having a tubular element 54 which contains the transducer 24 near its open end, as illustrated, arranged in fixed relationship to a larger diameter tubular member 56 which surrounds the structure 54 and provides an annular opening having substantially the same area in the annulus as is present in the tubular opening in element 54. A generally dished section 58 preferably is used to seal one end of the tubular member 56 as illustrated in FIGURE 16. The assembly of elements 54, 56 and 58 is preferably chosen such that the cross-sectional area around the bend remains essentially constant. The composite area comprising the center circular region plus the sealed annular region achieves in-phase sound radiation over the composite area similar to what was described in connection with the embodiment of FIGURES 15 and 16. In the arrangement of FIGURES 17 and 18, however, the structure is a simple single circle and will permit easier stacking when it is desired to combine a number of units into a large composite area for producing a sharp beam angle in the manner described previously.

In FIGURES 19 and 20 there is illustrated an arrangement of a special baffle structure for use in combination with the new transducer which combines the radiation from each end of the transducer and also increases the radiation resistance which is seen by the radiating faces of the transducer such that higher acoustic efiiciency is achieved for a transducer unit. Referring to FIGURE 20, the transducer 24 is shown mounted at the small diameter end of the tapered horn section 60. The face of the transducer 24 which is facing away from the tapered section 60 radiates through a tapered tubular section 62 and then through a flaring annulus section 64 formed as illustrated. The acoustic path length from the rear section of the transducer 24 around the flaring annulus 64 is made approximately /2 wavelength longer at the frequency of operation as compared to the acoustic path length from the face of the transducer 24 radiating into the tapered section 60. If the rate of flare of the axial opening in section 60, as well as the rate of 'fiare through the reverse tapered annular section illustrated in FIGURE 20, is made to follow approximately a logarithmic law, the radiation resistance at the faces of the transducer 24 may be increased considerably, as is well known in the art on loud speaker design. The advantageous embodiment of FIGURES 19 and 20 effectively provides an underwater exponential horn which includes an outer peripheral section in combination with an inner section and also provides that the passageway connecting the rear section of the transducer 24 through the tapered annular section is /2 wavelength longer than the passageway from the front section of the transducer to the mouth of the horn. In this manner, the phase of the radiation from the rear of the transducer is reversed such that it becomes of the same phase as that from the front section of the transducer when the combined radiation emanates from the concentric dual openings of the composite horn.

There has been shown and described hereinabove a unique electroacoustic transducer arrangement which is characterized by its efliciency of generating high power sound in deep water at lower or mid-audible range frequencies.

This new and improved transducer comprises a highly advantageous magnetic armature arrangement positioned within a sealed housing, and it is contemplated that the housing may be filled with a suitable inert gaseous medium such as nitrogen, helium and the like. In addition, it is contemplated that the transducer may be utilized in combination with the various unique baffle structures illustrated herein, either alone, in groups or in aligned axial arrays, as desired, all within the teachings of the present invention.

While there has been shown and described, several specific illustrative embodiments of the present invention it will, of course, be understood that various modifications and alternative constructions may be made without departing from the true spirit and scope of the invention. Therefore the appended claims are intended to cover all such modifications and alternative constructions as fall within their true spirit and scope.

What is claimed as the invention is:

1. The improvement of an electroacoustic transducer comprising a sealed housing formed of a tubular body having an end plate at each end thereof, a center plate having a pair of axially opposed faces, resilient means suspending said center plate for axial movement between said end plates, a first electromagnetic assembly having a portion mounted on one end plate and a portion mounted on one face of said center plate, a second electromagnetic assembly having a portion mounted on the other end plate and a portion mounted on the other face of said center plate, magnetizing coil means associated with each one of said electromagnetic assemblies, sealed electrical terminal means in said housing connected to each magnetizing coil means for enabling electrical connection to be established through said housing to said magnetizing coil means.

2. The improvement of an electroacoustic transducer in accordance with claim 1 wherein the end plates of said housing are formed with inner hollowed out portions to reduce the total weight of said housing while maintaining the resistance of said end plates to deformation when the transducer is submerged in deep water.

3. The improvement of an electroacoustic transducer and bafile assembly comprising a sealed housing formed of a tubular body having an end plate at each end there of, a center plate having a pair of axially opposed faces, resilient means suspending said center plate for axial movement between said end plates, a first electromagnetic assembly having a portion mounted on one end plate and a portion mounted on one face of said center plate, a second electromagnetic assembly having a portion mounted on the other end plate and a portion mounted on the other face of said center plate, magnetizing coil means associated with each of said electromagnetic assemblies, sealed electrical terminal means in said housing connected to each magnetizing coil means for enabling electrical connection to be established through said housing to said magnetizing coil means, and a tubular baffie enclosing said housing, said bafiie being approximately one half wave length long from one end plate of said housing to the open end of said bafile.

4. The improvement of an electroacoustic transducer and bafiie assembly comprising a sealed housing formed of a tubular body having an end plate at each end thereof, a center plate having a pair of axially opposed faces, resilient means suspending said center plate for axial movement between said end plates, a first electromagnetic assembly having a portion mounted on one end plate and a portion mounted on one face of said center plate, a

9 second electromagnetic assembly having a portion mounted on the other end plate and a portion mounted on the other face of said center plate, magnetizing coil means associated with each one of said electromagnetic assemblies, sealed electrical terminal means in said housing connected to each magnetizing coil means for enabling electrical connection to be established through said housing to said magnetizing coil means, and a tubular bafile enclosing said housing, said baffle having two open ends and being folded to effectively position said open ends in approximately the same plane.

5. The improvement of an electroacoustic transducer and baflle assembly comprising a sealed housing formed of a tubular body having an end plate at each end thereof, a center plate having a pair of axially opposed faces, resilient means suspending said center plate for axial movement between said end plates, a first electromagnetic assembly having a portion mounted on one end plate and a portion mounted on one face of said center plate, a second electromagnetic assembly having a portion mounted on the other end plate and a portion mounted on the other face of said center plate magnetizing coil means associated with each one of said electromagnetic assemblies, sealed electrical terminal means in said housing connected to each magnetizing coil means for enabling electrical connection to be established through said housing to said magnetizing coil means, and a tubular bafile enclosing said housing, said baffle being formed with two open ends and being folded to position said open ends in approximately the same plane and in coaxial relationship with each other.

6. In an electroacoustic transducer the combination comprising a base plate having a pair of opposite parallel plane surfaces, a first set of magnetic armature assemblies securely bonded to each of said plane surfaces, each of said armature assemblies having its unbonded surface poitioned in a plane parallel to the surface of said base plate, a sealed housing structure totally enclosing said base and armature assemblies, said housing structure having a pair of opposite end plates, a second set of magnetic armature assemblies bonded to the inner surfaces of said opposite end plates, the unbonded surfaces of said second set of magnetic armature assemblies lying in parallel planes and positioned closely adjacent to the plane surfaces of said first set of magnetic armature assemblies, spring spacer means attached between the opposite plane surfaces of said base plate and the inner surfaces of said opposite end plates of said housing structure, magnetizing coil means associated with each set of magnetic armature assemblies, sealed electrical terminal means connected to said magnetizing coil means and adapted to permit electrical connection to be established through the housing structure to the magnetizing coil means.

7. An electroacoustic transducer in accordance with claim 6 further wherein said sealed housing and end plates comprise inner cavities which reduced the weight of the housing structure while retaining the relatively high stiffness of the plates to resist bending of said plates when the transducer is submerged in deep water.

8. An electroacoustic transducer in accordance with claim 6 wherein said housing structure is cylindrical and said end plates are circular.

9. An electroacoustic transducer in accordance with claim 8 wherein each circular plate portion comprises an assembly of two mating hollowed sections whereby the composite plates are reduced in weight and retain a high stiffness to withstand deformation when the transducer is submerged in deep water.

10. An electromagnetic transducer comprising a sealed housing structure having positioned therewithin first magnetic means mounted for translatory vibration, second magnetic means attached to said housing structure and located in operable relationship to said first magnetic means, current coil means associated with each of said magnetic means, connection means for supplying electrical current to said current coil, and spring elements attached between said first and second magnetic means to hold said magnetic means in operable relationship to each other whereby translatory vibration of the housing structure will result in opposite phase to the translatory vibration of said first magnetic means whenever alternating current is supplied to the current coils.

11. An electromagnetic transducer in accordance with claim 10 further comprising a tubular baflie structure, means mounting said transducer with one face exposed to freely vibrate at one end of said tubular baffle structure, said tubular baffle structure being approximately one half wave length long from the opposite vibrating face of the transducer to the open end of the tubular baffle structure.

12. A plurality of electromagnetic transducers in accordance with claim 11 arranged in a spaced axial array whereby a directional beam of sound is achieved in a plane containing the axis of the spaced axial array when said transducers are driven from the same source of electrical current.

13. An electromagnet transducer in accordance with claim 11 wherein said tubular bafile structure is folded to effectively position both open ends of said tubular baflie structure in approximately the same plane.

14. The improvement of a transducer and baffle assembly comprising the combination of a transducer having a pair of opposite end faces and providing radiation from each of said end faces in opposite phase, a baffle structure comprising a first generally tubular member :having two openings, means mounting said transducer so that it may freely vibrate Within said first tubular member, one end face of said transducer being arranged approximately co-p laner with a first opening of said tubular member, a second tubular member surrounding and peripherally spaced from said first tubular member, said second tubular member having one end sealed by a rigid wall section, said sealed wall section being spaced from the second opening of said first tubular member and the open end of said second tubular member lying substantially in the same plane as the said first opening of said first tubular member.

15. An electromagnetic transducer in accordance with claim 14 wherein the path length difference between the second end face of the transducer to the open end of the second tubular member is approximately /z. wavelength of the sound wave at the operating frequency of the transducer.

16. In combination, a transducer providing radiation of opposite phase from a pair of opposite end faces, a baffle structure comprising a first generally tapered tubular member having a relatively small throat area at one end and a relatively large mouth area at the opposite end, a second flared tubular member having a relatively small throat area which is positioned adjacent to the throat area of said first tapered member, said second tapered member having an open mouth area which is larger than said first throat area, a third tapered tubular member having a relatively small closed end section and a larger open end section, said closed end section being spaced from said open end of said second flared tubular member.

17. The combination in accordance with claim 16 wherein said third tubular member forms a passageway having a tapered annular area which progressively increases from the small end of said tubular member to the larger open mouth end of said third tubular member.

18. The combination in accordance with claim 17 wherein the path length between the second radiating face of the transducer and the open free end of the annular passageway is /2 wavelength longer than the passageway through said first tapered tubular member at the frequency of operation of the transducer.

19. The combination in accordance with claim 17 wherein the rate of flare of the areas established by the tapered sections increases according to an exponentia l law.

20. The combination in accordance With claim 18 wherein the rate of flare of the areas established by the tapered sections increases according to an exponential law.

21. The improvement of an electroacoustic transducer and baflle assembly comprising a sealed housing formed of a tubular body having an end plate at each end thereof, an electromagnetic assembly positioned Within said sealed housing, magnetizing coil means associated with said electromagnetic assembly, sealed electrical terminal means in said housing connected to said mag- No references cited.

CHESTER L. JUSTUS, Primary Examiner..

LEWIS H. MYERS, Examiner. 

1. THE IMPROVEMENT OF AN ELECTROSTATIC TRANSDUCER COMPRISING A SEALED HOUSING FORMED OF A TUBULAR BODY HAVING AN END PLATE AT EACH END THEREOF, A CENTER PLATE HAVING A PAIR OF AXIALLY OPPOSED FACES, A RESILIENT MEANS SUSPENDING SAID CENTER PLATE FOR AXIAL MOVEMENT BETWEEN SAID END PLATES, A FIRST ELECTROMAGNETIC ASSEMBLY HAVING A PORTION MOUNTED ON ONE END PLATE AND A PORTION MOUNTED ON ONE FACE OF SAID CENTER PLATE, A SECOND ELECTROMAGNETIC ASSEMBLY HAVING A PORTION MOUNTED ON THE OTHER END PLATE AND A PORTION MOUNTED ON THE OTHER FACE OF SAID CENTER PLATE, MAGNETIZING COIL MEANS ASSOCIATED WITH EACH ONE OF SAID ELECTROMAGNETIC ASSEMBLIES, SEALED ELECTRICAL TERMINAL MEANS IN SAID HOUSING CONNECTED TO EACH MAGNETIZING COIL MEANS FOR ENABLING ELECTRICAL CONNECTION TO BE ESTABLISHED THROUGH SAID HOUSING TO SAID MAGNETIZING COIL MEANS. 